you Can use this code.....
Const ARR_SIZE_X As Integer = 9999999
Const ARR_SIZE_y As Integer = 5
Dim a2(ARR_SIZE_y, ARR_SIZE_X) As Double
For y = 0 To ARR_SIZE_y
For x = 0 To ARR_SIZE_X
Redim preserve a2(ARR_SIZE_y,ARR_SIZE_X)
a2(y, x) = a1(x)
Next
Next